This invention relates to injection molding and more particularly to an improved heated nozzle probe and a stack molding system incorporating it.
Elongated nozzle probes having internal electrical heaters are well known for use in injection molding. Normally, the heated probe is seated to extend into the melt passage and the pressurized melt flows around or along it to the gate. An early example of this is shown in U.S. Pat. No. 3,970,821 to Crandell which issued July 20, 1976. Another example is disclosed in the applicant's U.S. Pat. No. 4,376,244 which issued Mar. 8, 1983 in which a heater member is cast into a well in an outer body. Yet another example of a nozzle probe is shown in Japanese Utility Patent Application No. 57-69184 to Yoshida filed Oct. 11, 1980. More recently, the applicant's U.S. patent application Ser. No. 453,572 entitled "Method of Manufacture of an Injection Molding Integral Heated Probe" filed Dec. 27, 1982, and now abandoned, discloses an improved nozzle probe in which the melt flows through externally open melt channels and a thermocouple extends into the copper filler to more accurately measure the temperature adjacent the tip end.
As mentioned in these previous patents and applications, it is also well known that temperature control of the melt as it flows along the nozzle probe and particularly in the gate area is critical to the successful operation of the system. Despite this fact, almost all of these previous nozzle probes disclose only the use of a single heating element to maintain and control the temperature of the melt flowing along to the gate.
The applicant has now unexpectedly discovered an improved nozzle probe having two separate heating elements which provides improved temperature control, as well as improved apparatus for stack molding which utilizes these nozzle probes and does not require a valve gate. Valve gated stack molding is known in the art, as shown by the applicant's U.S. Pat. No. 4,212,626 which issued July 15, 1980. U.S. Pat. No. 3,800,027 to Tsutsumi which issued Mar. 26, 1974 does show a nozzle probe with two separate heaters or heating elements. However, in order to control the flow of melt through the gate it is necessary to intermittently energize one of the elements which extends into the gate according to a predetermined cycle. While this is satisfactory for some applications, it has the problem that cycle speed is limited by the time it takes the element to heat and cool.